This invention relates to automatic print cartridge alignment system to correct the positional offset of the cartridge of a bidirectional printing device.
There are several known methods for compensating the errors of a cartridge. A traditional method is for a user to view a test pattern and to adjust for the best printout. The adjustment is then set. This method has been disclosed in U.S. Pat. No. 4,818,129 and Japanese patent No. 61-76372, where correction have been preset in the cartridge and no automatic correction capability are provided. Another method has been disclosed in U.S. Pat. No. 5,044,796 (Republic of China patent No. 151002), which first analyzes the content to be printed and then determines the best adjustment for least amount of offset for the bidirectional printing. Although this method can increase the throughput, it also does not have the capability of automatic compensation, and is suitable only for sparse printing content. For dense printing content, this method only has the unidirectional printing capability. Still another method, as disclosed in U.S. Pat. Nos. 5,289,208, 5,250956 and Japanese patent 62-227757, relies on actual printing to detect the actual amount of offset. The offset sensing system utilizes an analog-to-digital converter and an amplifier, together with light source and lenses. The sensing circuit is relatively expensive. Furthermore, since actual printing of a test pattern is required to determine the offset, the method is not suitable for manufacturing production.
Tazaki disclosed in U.S. Pat. No. 4,345,263 a print carriage, which uses a linear motor and an optical ruler to feedback and determine the position of the print cartridge. Due to limitations of the optical ruler and its sensor, the accuracy of the system is limited. The best resolution which Tazaki""s system can achieve is the pitch between the slots of the optical ruler.
Tanuma disclosed in U.S. Pat. No. 4,818,129 a print cartridge, which is incapable of automatically detecting the offset between two opposite directions of printing. Two rows of test patterns of vertical lines orthogonal. to the movement of the carriage must be scanned. The first row is for forward scan, and the second row is for reverse scan. Time delay or advance is introduced manually to align the corresponding vertical lines in the two rows. The required time delay or advance for correction of each pair of vertical lines is stored in a wire matrix. The alignment is done by user""s eye and therfore not automatic.
An object of this invention is to provide a method and system for automatic alignment of cartridge for bidirectional printing. Another object of this invention is to increase the operating speed of bidirectional printing. Still another object of this invention is to provide automatic alignment of cartridge during manufacturing without actual printing a test pattern. A further object of this invention is to provide an automatic cartridge alignment system for bidirectional printing, which is low-cost, highly accurate, simple in structure and suitable for mass production.
These objects are achieved in this invention by sensing the actual position of the printing cartridge with respect to its theoretical position. The required compensation for corrrecting the offset error is then calculated and used to control the printing cartridge. For finer control, time delay may be used in addition to adjusting the position of the cartridge.